28 BIOLOGY AND TECHNIQUE 



induced to grow in indifferently anaerobic environment. Ferran/ 

 moreover, succeeded in gradually adapting the tetanus bacillus to an 

 aerobic environment. In this case, however, the virulence of the bacil- 

 lus was lost. 



Nitrogen. — ^The nitrogen required by bacteria is taken, in most cases, 

 from proteids. Most important in this respect, of course, are the dif- 

 fusible proteids; but many of the non-diffusible albumins may be 

 rendered assimilable by the proteolyzing enzymes possessed by many 

 microorganisms. Among the pathogenic, more strictly parasitic bac- 

 teria, moreover, a delicate specialization may be observed as to the 

 particular varieties of animal albumin which may be utilized by them. 

 Thus the gonococcus grows more readily only upon uncoagulated human 

 blood serum; the Pfeiffer bacillus requires hemoglobin, and the diph- 

 theria bacillus outgrows other bacteria upon a medium composed for 

 the greater part of coagulated beef serum. For bacteria that do not 

 absolutely require native animal proteid for their development, the 

 most common nitrogenous ingredient of culture media is pepton, added 

 in solutions of varied concentration. 



A large number of bacteria (pathogenic and saprophytic), on the 

 other hand, may thrive on media containing absolutely no proteid, in 

 which case, of course, a sjmthetic proteid production by the micro- 

 organisms must be assumed. A medium which has been extensively 

 used to demonstrate this phenomenon is that devised by Uschinski,^ 

 containing ammonium lactate, glycerin, asparagin (the amide of amido- 

 succinic acid), and inorganic salts. 



Creatin, creatiain, urea and urates, and even ammonia compounds 

 and nitrates, may serve as adequate sources of nitrogen for many of the 

 less parasitic bacteria. A limited number of species, moreover, the bacilli 

 in the root tubercles of the leguminosse and the nitrogen-fixing organ- 

 isms of the soil, possess the power of obtaining their supply of nitrogen 

 directly from the free Nj of the atmosphere. 



Although the sources of carbonaceous and of nitrogenous food supply 

 have been separately treated in the preceding paragraphs, it should not 

 be forgotten that, in many instances, both elements are taken up within 

 the same compound, and that separate supplies are a necessity in isolated 

 cases only. 



Hydrogen. — Hydrogen is obtained by bacteria largely in combina- 



i Ferran, Cent. f. Bakt., I, xxiv, 1898. 

 » Uschinski, Cent. f. Bakt., I, xiv, 1893. 



